The present invention relates to grinding machines, in particular grinding machines for restoring a relief angle on the part-helical rotary blades of grass mowers of the type having a cylindrical cutting unit. The invention also provides a method of restoring a relief angle on the part-helical rotary blades of a reel mower.
Cylinder or reel mowers comprise one or more cylinders or reels bearing a plurality of part-helical blades and mounted for rotation about a horizontal axis transverse to the direction of motion of the mower. Each cylinder or reel cuts the grass in co-operation with an elongate bottom blade, commonly referred to as a bedknife, which is disposed alignment with the reel and positioned for the grass to be positioned accurately allowing the helical blade to cut the grass in a transverse scything motion. The faces of the rotary blades become worn during grass cutting and are required to be sharpened periodically by grinding. After repeated sharpening, the relief angle ground into the cutting face of the blade when it was manufactured is removed, thus potentially compromising the efficiency of the mowing process. The present invention prolongs the life of the rotary blades by grinding or restoring the relief angle.
Known grinders comprise a grinding wheel movable to and fro along a guide rail whilst rotating to grind the front face of a rotary blade. In order to grind the rotary blades of a mower with such known machines, the reel must be removed from the mower and mounted on the grinder; alternatively the mower or, especially in the case of tractor mounted mowers, a disassembled part thereof, must be placed on the grinder.
Prior art blade grinders, therefore, have required the mowing machine or a part of the mowing machine to be taken to the grinder. Tractor mounted mowers, and often walking mowers, have had to be disassembled to permit the reel or a part of the mowing machine including the reel to be placed on the grinder.
One example of a portable device capable of in situ grinding is disclosed in U.S. Pat. No. 2,245,968 to Erdman. This device is slidably mounted to a bar fitted to the mower to enable a reciprocal grind motion along either the bedknife or rotary blades of a mower. The device has a releasable slide mechanism to adjust the angle of grind on the blade and screw adjustment to vary the grinding depth.
The present invention seeks to provide a portable grinding machine for grinding a relief angle onto a rotary blade incorporated in cutting apparatus. The grinding machine can therefore be mounted on the cutting apparatus with the machine and the cutting apparatus in suitable relative disposition for grinding of the blade without prior disassembly or adjustment of the cutting apparatus, i.e. the blade can be ground whilst the cutting apparatus is in a complete and assembled state and no special changes and only minimal adjustments need to be made to the complete mower.
According to one aspect of the invention, there is provided a portable grinding machine for grinding or restoring a relief angle onto the rotary blades of a grass mowing machine in a transverse reciprocal movement which grinding machine comprises a blade support means for automatically maintaining the rotary blades of said mowing machine in contact with the grinding wheel during the reciprocal movement of the grinding machine along a blade.
According to an optional feature of this aspect of the invention the blade support means is adapted to retain the blade between said finger and the grinding wheel. Optionally, said guide means is adjustably mounted relative to the grinding wheel by first adjustment means to accommodate blades of different. Preferably, the guide means terminates in a roller which contacts the underside of the blade.
According to another optional feature of this aspect of the invention the blade support means is resiliently biased relative to the grinding wheel such that increased force applied to the grinding machine in a direction perpendicular to the direction of grinding results in a greater grinding depth.
In yet another optional feature of this aspect of the invention the grinding machine is handheld.
In yet another feature of this aspect of the invention a guide r ail is provided with opposite ends, a grinding wheel assembly is provided for receiving said portable grinding machine, which assembly is mounted for movement to and fro along, said guide rail, and said guide rail has readily releasable attachment members for releasably securing the grinder on the mowing machine such that when said grinding wheel is moved along said guide rail the grinding wheel can move along a blade face of said rotary blade and grind it. Optionally, first adjustment means is provided to adjust the position of said guide rail adjacent its opposite ends relative to said rotary blade, and second adjustment means being provided to adjust said grinding wheel assembly relative to said guide rail and hence relative to said blade face of said rotary blade.
According to an optional further feature of this aspect of the invention, the first adjustment means includes means for varying the position of said attachment member in a first direction perpendicular to the longitudinal axis of the guide rail. Preferably, the first adjustment means comprises one locking lever secured to each attachment member, and slidable within a respective slotted bracket, said slotted brackets being secured to said guide rail. Preferably, the second adjustment means comprises adjustment means in a second direction perpendicular to the longitudinal axis of the guide rail. Preferably, the second adjustment means adjusts the depth of grinding.
In to a another optional feature of this aspect of the invention the second adjustment means comprises a slidable locking means and a rotary control knob attached to a threaded feed screw.
In yet another optional feature of this aspect of the invention the angle of grind: is controlled by adjusting the first and second adjustment means.
In yet another optional feature of this aspect of the invention the attachment members are magnets.
A second aspect of the of the invention provides a method of grinding a relief angle onto a rotary blade of a reel mower, comprising orienting the complete mower to expose the rotary blades, attaching to the mower a portable grinding machine which comprises a guide rail, a grinding wheel assembly receiving a rotary grinding wheel which assembly is mounted for movement to and fro along said guide rail, including the steps of adjusting attachment means to orientate said guide rail relative to a reel on which the rotary blades are mounted so that it is substantially parallel to the axis of the reel and adjusting said grinding wheel assembly to introduce said supporting means to maintain contact between the grinding means and a single rotary blade so that the relief angle of the rotary blade can be ground throughout its length by allowing the reel to rotate as the grinding wheel assembly is moved along the length of the guide rail, repeating the process until all of the blades mounted oil the mower reel have been ground.
According to a third aspect of the invention, there is provided a method of grinding a relief angle onto a rotary blade of a reel mower comprising orienting the mower to expose the rotary blades adjusting a finger mounted on a grinding machine to retain the blade between the finger and a grinding wheel, removing the grinding machine away from contact with the blade, starting the power until connected to the grinding wheel, trapping the blade between the finger and the grinding wheel, and commencing grinding in a reciprocating transversing motion, applying a force to the grinding machine has ground the blade to the required depth, repeating the process until all of the blades mounted on the mower reel have been ground.